A top law firm has launched an investigation into a bogus memo that claims to have come from the company advising the public on paying the household charge.

Dublin-based McCann Fitzgerald has informed people who received the memo via email and leaflet drops that it has nothing to do with the firm, even though it contains its logo and website address.

The fake advice relates to the Government's 100 euro household tax, which was rolled out at the start of the year.

A McCann Fitzgerald spokesman advised the media not to print details of the memo, which claims the statute implementing the charge cannot affect members of the public if they do not consent to it. He said: "The memorandum/email is not a McCann FitzGerald document, it has not been prepared by the firm and it does not express a legal opinion of the firm."

The firm is trying to find out how its name came to be associated with the document, which has been circulating the internet and social media sites this week.

The Government introduced the flat household tax on January 1. Each house is required to register for the charge by March 31 and must pay 100 euro for the year. The Government hopes to raise 160 million euro by the end of 2012 - money that will fund public services, including footpaths, parks and libraries.

So far only 109,569 households have registered, generating just over 10 million euro. Around 1.5 million homes have just over a month to sign up to the tax or risk a court appearance. The Government has insisted the charge is only temporary and that a property tax will eventually be introduced.

A group of TDs and councillors objecting to the tax has distanced itself from the memo and said it informed the law firm its name was being used illegitimately.

The Campaign Against the Household Charge, spearheaded by People Before Profit TD Richard Boyd Barrett, has advised the public to ignore the information in the emails and leaflets, saying it is legally incorrect.

Spokesman Gregor Kerr said: "The campaign is very concerned that people are believing this information. It's very important that in standing together we will resist this charge, with mass co-operation in the communities. The information in these emails goes against what the campaign stands for."